The systematic investigation and delineation of the in vivo and in vitro responses of transplantable malignant neoplasms and their components (parenchyma and vasculature) as well as the respones of dose limiting normal tissues to ionizing radiation and drugs administered separately or in combination in various temporal modes for the determination of potential positive interactions between these therapeutic modalities in the treatment of cancer and for the optimization of therapeutic ratios in the normal tissue at risk.